So if he texts, "I'm sorry I am not going to be in for work today I am receiving medical treatment from my mental health provider," that should be public records?
If he emails, "I am sorry Mrs. Channing, but there is no work you can do in Physics 102 to avoid a failing grade," that should be public record?
Releasing the first email would be a violation of federal law (respecting medical confidentiality) and the second one would likely violate State law or university code on student confidentiality.
The Supreme Court has ruled that American citizens have a reasonable expectation that the contents of their email will be kept private, just like their phone conversations.
But he didn't make that argument -- the argument that some of the emails should be withheld because they have private information. He made the argument that emails discussing the data relating to climate models should be withheld because they contain proprietary information that could cause the university to be less competitive with other universities in obtaining funding. That's completely different. And if he made the argument you made I might agree with him, but he made a different argument that I disagree with.